Polar mode observations are being carried out on experimental basis since
GTAC Cycle 9. For more details, please contact Dr. Jayaram Chengalur (chengalu@ncra.tifr.res.in)

RUNNING THE NEW CORRELATOR MODES:

A number of new correlator data acquisition modes are now
available for test. These modes include:

(1) Full stokes (in either USB or LSB),
(2) 256 channels in RR and LL (in either USB or LSB) for all
baseband bandwidths 16 MHZ or smaller
(3) identical data being piped through both halves of the
correlator (either for possible SNR improvements, as
routinely used elsewhere, or for testing)
(4) In addition of course, the old "Indian Polar" mode
continues to be supported.

Introduction of these modes has required a change in the lta
format. Existing binaries of programs like ltahdr, xtract,
gvfits etc. will be unable to read the new data files.
Modified versions of all these programs which will read the
new as well as the old format are available.

There has also been a substantial change in the way in which
users initialize and reconfigure the correlator and das
software. Rather than having to consistently edit several
text files on several different PCs and supply consistent
command line options, users now run a single program that
guides them through a menu. (The menu is a clunky old text
based one, volunteers to produce something more fancy are
welcome). This program runs on the ONLINE machine ("aditya")
and produces a parameter file ("/temp2/data/corrsel.hdr").
Wrappers running on aditya read this file and will
initialize/reconfigure the correlator as appropriate for the
selected observing mode. Information required for
configuring acq30, dlytrk etc is also taken from this same
file and transferred to appropriate locations by dassrv.
This entire operation of transfer of parameters is
transparent to the user.

Step by step instructions for running the new modes, looking
at the data in real time, or offline, and converting to FITS
follows:

INSTRUCTIONS FOR RUNNING THE NEW CORRELATOR MODES:
--------------------------

1. log in to corracqa, corracqb, corrctl as observer and run
"setdvl" on each PC. (This sets the paths and environment
variables appropriate for the new "development" software.
NB: if there are any shared memories floating around from
the older das versions, you will need to delete them).

2. login in to mithuna and mithunb as observer and chose "d"
when promoted for which software system to use. (Again,
this sets the paths and environment variables appropriate
for the new "development" software. NB: if there are any
shared memories floating around from the older das
versions, you will need to delete them).

3. login into aditya as observer, and cd to
/home/observer/dassrv-tst

4. If you want to initialize the correlator, run corr init
on *aditya* (This will run corr_config and newdly_config
on the corrctl PC).

5. Choose the observing setup by running corrsel on *aditya*
(This will setup the file /temp2/data/corrsel.hdr, which
contains information on how you want the correlator
configured. corrsel allow a menu based selection of the
observing mode, integration time, clksel etc.

Again the names should be self explanatory. In addition, the
mode can be a string of the form dpc_abcd, where 0<= a,b,c,d
<=3. A mode of the form dpc_abcd means that the dpc mux
sends channel a data to where channel 0 data normally goes,
channel b data to where channel 1 data normally goes and so on.)

6. Reconfigure the correlator to the selected mode. To do this type

corr reconf on *aditya*.

7. start acq, acq30, sockcmd fstop, dlytrk,dassrv,collect on
the appropriate machines. (acq can be running when you
reconfigure the correlator, but as before, dlytrk and
fstop should be stopped). Note that none of the programs
need command line options, but instead, as explained in
the introduction, will automatically understand the
selected observing mode.

NB: The acqs on corracqa and corracqb should be started
within 1 STA cycle
(i.e. 128 ms!) of each other. The easiest way to do this is:
(a) export the corracqa acq window to all desktops.

(b) go to the corracqb desktop and align the corracq and
corracqb acq windows one below the other

I agree that this is a pretty silly way to do things. A
more automatic method is in the prorverbial pipeline.

8. Ask the operator to give an init and add a project from
the master terminal. The bandmask while initing and
adding a project should be correspond to the chosen mode.

NB: The bandmask is a bit mask with bits in the order USB130
USB 175 LSB130 LSB175.
For a pure USB observation the bandmask is 3 (e.g. UsbPolar,
UsbCopy, AllU130..)
For a pure LSB observation the bandmask is 12 (e.g. LsbPolar,
LsbCopy, AllL130..) For a dual sideband observation the bandmask
is 15 (e.g. IndianPolar). It may be possible that putting
bandmask to 15 will work for all modes, but I have not verified.

9. start and stop scans, record as usual. DO NOT USE MEDIAN
FILTER - I HAVE NOT FIXED THE TIME STAMPS IN MEDIAN FILTER YET.

10. The only way to look at the data in real time is
Manish's new dasmon. You have to run a modified version of
this program which is in /home1/manish/new_dasmon/dasmon on
mithuna and mithunb. NB: In the new modes the data is
divided between the two halves of the correlator. For
example in the UsbPolar mode U130xU130 and U130xU175 come in
mithunb (i.e. the "ltb" file) while U175xU175 and U175xU130
come in mithuna (i.e.the "lta" file). Hence (a) dasmon in
mithuna or mithunb will only show you one half of the data
(b) "normalization" cannot be applied in some modes. To
normalize U130xU175 one needs the U130 and U175 selfs, but
both will be available only when one merges the data streams.

11. ltahdr and other lute programs will not work. Instead
use tltahdr (tltahdr is backward compatible, but I plan a
proper upgrade only after a bit more testing).

12. tax and xtract will not work, instead use ttax and
txtract. Please remember that each file has only half the
data. The programs do internally consistent things, but you
need to be aware of what you are doing. Avoid normalization
in txtract, of course.

13. you can merge the lta and ltb files using tltamerge.
This merged file will have the complete data, and is easier
for playing around with ttax and txtract.

14. the merged file can be converted to FITS using tlistscan
and tgvfits. The individual files can also be converted
using these programs, but I don't seem to be able to get
AIPS to understand the polarizations in a file with only RR
RL or only LL LR. I think that only some partitioning
produced by the VLA correlator is understood. The combined
RR RL LR LL FITS file is interpreted without problem.

taxx - For true polarization lta files. taxx
output is easiest to understand when it is run on a merged (USB and LSB
merged) lta file.

All the other offline programmes work on either IndianPolar or true
polarization lta files.